Deflection system for relatively shallow cathode ray tube



Nov. 2, 1965 5, v ETAL 3,215,888

DEFLECTION SYSTEM FOR RELATIVELY SHALLOW CATHODE RAY TUBE Filed Feb. '7, 1963 1 FIG.|

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United States Patent 3,215,888 DEFLECTION SYSTEM FOR RELATIVELY SHALLOW CATHODE RAY TUBE Svend E. Havn, Liverpool, and Mooshi R. Namordi, Syracuse, N.Y., assignors to General Electric Company, a

corporation of New York Filed Feb. 7, 1963, Ser. No. 256,971 6 Claims. (Cl. 315-21) This invention relates to an image display system and in particular to means for energizing a relatively shallow cathode ray tube.

With the desire to provide a compact image display system, particularly in the field of commercial television, has come the development of cathode ray tubes wherein the electron beam is caused to change course radically in a comparatively short distance. One example of such cathode ray tube developments is the relatively shallow tube that is the subject of the US. patent application Serial No. 141,862, filed September 29, 1961, and assigned to the assignee herein, now Patent No. 3,155,872. In such a system normally at least one controlled deflection, generally the vertical deflection, is accomplished by a variable electric field. The electric field is varied, to provide a full range of deflection or a scan, in response to a controlled voltage having a great peak-to-peak voltage excursion as needed to establish the requisite variations of electron path.

Generation of a controlled voltage having a great peakto-peak voltage excursion presents a serious obstacle to providing an economical compact image display system. The required voltage excursion is often in excess of many thousands of volts and generally must be accurately synchronized with an information-carrying signal to provide a useful device. While means for generating economically high direct-current voltages of relatively constant magnitude are well known, for example, the high voltage generator in most commercial television receivers; and means for economically switching such high direct-current voltages are well known, for example, the thyratron; there is presently no known means for providing economically an accurately synchronized controlled voltage having the great peak-to-peak voltage excursion needed for electric field deflection in compact image display systems.

Accordingly, it is one object of this invention to provide for a compact image display system a control voltage having a great peak-to-peak voltage excursion.

It is another object of this invention to provide a shallow cathode ray tube system having an improved vertical deflection voltage generator.

Still another object of this invention is to provide an improved compact image display system having means for providing economically an accurately synchronized control voltage having the great peak-to-peak voltage excursion needed for electric field deflection in such systems.

Briefly, in accordance with one form of this invention, high voltage switching means is provided to selectively connect the electric field deflection section of a shallow cathode ray tube to a source of direct-current high voltage in response to a predetermined signal. The field is thereby charged to a predetermined maximum high voltage, at which time the switching means ceases to be conductive. An electron target of material having low secondary emission is disposed adjacent the normal path of the electron beam, and deflection means are provided to direct the electron beam to the target during a predetermined portion of each horizontal scanning cycle. The target is electrically connected to the deflection means, and reduces the potential thereof each time that electrons are deposited on the target. The potential of the deflection means is thereby reduced by predetermined voltage increments during each horizontal scan cycle to provide a corresponding variation in the electric field and the path of the electron beam. At the termination of a complete vertical scanning of the screen of the display device, the high voltage means is triggered and the cycle repeats as before.

The invention will be explained in more detail in connection with the drawings in which:

FIGURE 1 is a schematic diagram of the front view of a shallow cathode ray tube system; and

FIGURE 2 is a schematic diagram of the side view of a shallow cathode ray tube system.

In the specific cathode ray tube selected for illustrative purposes in FIGURES 1 and 2, an electron gun 2 projects a beam of electrons 3 through a magnetic deflection means generally shown at 4. The magnetic deflection means is responsive to the voltage supplied from source 5 of horizontal deflection voltage, as conducted by leads 6 and 7, to deflect electron beam 3 from one extreme path 8 through undeflected path 9 to the other extreme path 10. The electron beam passes through collimating and focusing means 12, which is preferably of the type which is disclosed in the US. patent application Serial No. 141,863, filed September 29, 1961, and assigned to the assignee herein. The beam emerges from collimating and focusing means 12 in any one of several spaced parallel paths, such as 14, 15 or 15'.

In order to provide vertical deflection of the electron beam, the electron beam emerges from collimating and focusing means 12 into a beam deflection means comprising an electric field defined by electron-permeable conductive coating 16 on the screen, and spaced voltage gradient means, generally shown at 17. The voltage gradient means is shown schematically as a plurality of serially disposed resistors, such as resistors 18, supplying a suitable voltage to a plurality of spaced parallel conductive wires, such as wires 19. In a preferred embodiment, however, voltage gradient means 17 comprises a highly resistive coating disposed in a plane spaced rearwardly of and substantially parallel to conductive coating 16 with highly conductive means establishing equipotential lines at the top and bottom surfaces thereof.

Suitable static operating potentials are supplied to the vertical deflection means by a direct-current voltage source 20, which is electrically connected to conductive coating 16 by conductor 21, and direct-current voltage source '22 which is connected to the upper edge of voltage gradient means 17 by conductor 23.

The above described detailed explanation of a specific type of shallow cathode ray tube is intended merely to serve as a suitable setting and background in which the present invention, as described hereinafter, is placed to aid understanding thereof. It is to be understood that the previously described specific cathode ray tube, the details of which form no part of the present invention, is used merely for illustrative purposes and the scope of this invention is not limited thereto.

In accordance with the present invention, in a preferred embodiment thereof, a high voltage switching device 25 is provided. The cathode 26 of switching device 25 is electrically connected to the lowermost portion of voltage gradient means 17 Switching device 25 may be any of a large number of well known means for providing a controlled discharge, including, for example, thyratrons and triggered vacuum discharge devices. It is only required that there be a highly conductive path intermittently established between the anode 27 and cathode 26 in response to a trigger signal introduced by an appropriate grid or firing electrode, such as 28.

Further energizing power for voltage gradient means 17 is supplied by source 29 of relatively high directcurrent potential. The positive terminal or source 29 is electrically connected to anode 27 of switching device 25. While source 29 could be a battery, as indicated schematically, preferably, source 29 takes the form of a high voltage rectifier and filter network which is supplied high voltage alternating current from a transformer, such as the flyback transformer generally used in the field of commercial television for this purpose.

In order to vary the voltage of gradient means 17, a target 30 of material characterized by low secondary emission of electrons is disposed adjacent the normal path of the electron beam. Target 30 is electrically connected to cathode 26 of switching device 25 and the lower portion of voltage gradient means 17. Auxiliary beam deflecting means are provided intermediate target 30 and electron gun 2 to direct beam 3 to target 30 in response to a predetermined signal. Preferably, the auxiliary deflecting means takes the form of spaced parallel plates 32 and 33. One of the plates, such as 32, is grounded and the other plate, such as 33, is electrically connected to a source of voltage pulses.

In this specific embodiment, the predetermined signal is a pulse supplied by the source of horizontal synchronizing pulses generally associated with such image display systems. Spaced plates 32 and 33 are oriented with respect to beam 3 such that the presence of a positive voltage pulse appearing on plate 33 causes beam 3- to follow path 34, thereby impinging on target 30 rather than traveling upwardly through collimating and focusing means 12. The electrons transferred to target 30 reduce the voltage of target 30 and voltage gradient means 17 which is connected to target 30.

Operation is as follows: a narrow low frequency pulse of suitable polarity is applied to control electrode 28 of switching device 25, when it is desired to commence a vertical scan of the screen. Preferably, the narrow low frequency pulse is derived from a source of vertical synchronizing pulses, commonly associated with image display systems, in order to insure synchronization of the scan with information usually modulated on the electron beam. Switching device 25 then fires, or becomes conductive, and cathode 26, target 30 and the lower portion of voltage gradient means 17 rapidly approach the high positive direct-current potential of source 29.

When the lower portion of voltage gradient means -17 attains substantially the voltage magnitude of source 29, the vertical deflection is as shown by electron beam path 14, and the beam impinges upon the uppermost portion of the screen. Also, when cathode 26 of switching device 25 nears the potential of anode 27 thereof, the device ceases to be conductive. The aforementioned behavior is largely characteristic of thyratron-like devices,

and it is to be understood that appropriate amplifier-type devices may be used also in which case they would become non-conductive upon termination of the narrow low frequency vertical synchronizing pulse.

Thereafter, each time that the electron beam impinges upon target 30, in response to a predetermined signal supplied to the auxiliary deflection system, the voltage magnitude of gradient means 17 is reduced. The beam is thereby caused to impinge upon the screen at a lower vertical position upon termination of the predetermined signal. By providing a predetermined signal of relatively high frequency pulses, the electron beam vertically scans the screen in increments during the interval between pulses from the source of narrow low frequency pulses.

In the usual image display system, having a screen adapted to provide a visible phenomenon in response to excitation by an electron beam which vertically scans the screen at a low frequency rate and horizontally scans the screen at a relatively high frequency rate, there are a plurality of suitable sources of relatively high frequency pulse which may be connected to the auxiliary deflection system of this invention, For example, the electron beam may be directed to target 30 between horizontal scans of the screen by supplying to the auxiliary deflection system pulses from the fly-back transformer, pulses from the source of horizontal blanking pulses or, pulses from the source of horizontal synchronizing pulses. The latter has been selected in the schematic diagrams, for illustrative purposes.

When a pulse from the source of relatively high frequency pulses causes a sudden variation in voltage of plate 33, of the auxiliary deflection system comprising plates 32 and 33, the course of electron beam 3 is changed to a path such as 34 wherein the beam impinged upon target 30. The voltage of the lower portion of voltage gradient means 17, which is connected to target 30, is thereby lowered by an amount dependent upon the capacity of voltage gradient means 17 to store charge, the number of electrons which impinged upon target 30 and the effectiveness with which secondary emission of electrons by target 30 is prevented.

The amount by which the voltage of voltage gradient means 17 is lowered determines the vertical spacing between successive horizontal scans. The minimum capacity of voltage gradient means 17 is substantially fixed, for practical reasons, by the structure of any particular tube. The capacity may be easily increased to any desired value merely by adding a suitable high voltage capacitor to the system, such as from cathode 26 to ground. Also, it is possible to accelerate voltage discharge by providing an additional leakage path, such as by using a high resistance connected from cathode 26 to ground. The latter expedient, however, introduces a non-linearity in the control voltage which may, or may not, be desirable.

The number of electrons striking target 30 depends upon the interval during which the beam is directed to target 30, as determined by the pulse width of the relatively high frequency pulses, and the intensity of the beam, as determined by the modulation of electron gun 2 during the interval of interest. The efficiency with which target 30 collects electrons and prevents secondary emission can be varied by changing the material of target 30.

The deflection of beam 3 along path 34 a described occurs during each retrace or flyback portion of a horizontal scan, and consequently a net charge is subtracted from voltage gradient means 17 after each horizontal scan. Since the beam intensity during horizontal flyback can be easily controlled, the number of electrons striking target 30 during successive horizontal flyback intervals can be varied as desired. Therefore, if a nonlinear potential variation is required at the lower end of gradient means 17 to obtain a linear vertical scan, proper electron beam modulation (control) during the horizontal flyback interval will achieve the desired vertical scan linearity. By this means the potential of the lower portion of voltage gradient means 17 is incrementally reduced to a value wherein the electron beam scans a path, such as 15', along the lowermost portion of the screen. At the completion of a series of horizontal scans defining a complete raster, a vertical synchronizing pulse is again applied to control electrode 28 and switching device 25 is again triggered, or fired, to provide another vertical scan as previously described.

The advantages derived from practicing the present invention are many, and, of course, the order of importance may vary depending upon the specific image display system with which it is used and the particular application to which the system is put. First, by using the subject invention it is possible to provide a controlled voltage having great peak-to-peak voltage excursion with a very minimum of circuit components. In most cases, only switching device 25 need be mounted externally of the cathode ray tube, and this by itself greatly lessens the safety and reliability problems associated with control of high voltages. Second, in many systems the rapid deflection of the electron beam out of the path wherein it strikes the screen during retrace or flyback obviates the use of a horizontal blanking pulse. Third, the vertical deflection field, as determined by voltage gradient means 17, is constant during each horizontal scan of the target, thereby eliminating any transient influences which the vertical deflection field might otherwise have upon the electron beam during a horizontal scan.

It should be noted that the required potential waveform on the lower end of gradient means 17 to obtain a linear vertical scan is substantially determined by the geometry and potentials of deflection means 16 and 17. It is possible that there exists a geometry to which appropriate potentials applied will require an exponentially decaying potential at the lower end of gradient means 17 for the electron beam to linearly scan the screen in the vertical direction. For such a configuration, deflection means 32 and 33 and target 30 are excluded while a proper resistive coating is applied at gradient means 17 and a proper high voltage capacitor is connected to the lower end of gradient means 17 so as to give the appropriate RC time constant required. This time constant is usually in the order of 15.7 milliseconds for television fields.

Although this invention has been described and shown in conjunction with a specific cathode ray tube system, the details of this system form no part of the present invention, and the present invention is not limited thereto. While the present invention has been described with reference to an auxiliary electric field deflecting means, and the electron collecting target is shown disposed between the collimating means and the usual horizontal deflection means of a cathode ray tube, it is to be understood that this invention is in no way limited to the use of electric auxiliary field deflecting means or such a target location. For example, magnetic auxiliary deflecting means may be preferable in some applications, particularly in systems wherein the horizontal deflection means is an electric field, rather than a magnetic deflection means as illustrated. The auxiliary deflecting means and target of the subject discl0sure could be equally well located in other convenient locations within the tube, for example, between the electron gun and the horizontal deflection means. Also, while the plate 32 of FIGURE 2 is shown schematically as being grounded, it is possible to utilize plates 32 and 33 as focusing or accelerating electrodes, in which case other suitable quiescent potentials may be applied to plates 32 and 33. Therefore, it is intended that the appended claims include the many modifications and variations of the present invention which will suggest themselves to those skilled in the art and fall within the true scope and spirit of this invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is as follows:

1. In a compact image display system having a cathode ray beam, horizontal beam deflection means, vertical beam deflection means including voltage gradient means arranged to position said beam in dependence upon the voltage of said gradient means, a source of low frequency pulses, a source of higher frequency pulses and a source of direct-current voltage, the improvement comprising:

(a) means responsive to the pulses from the source of low frequency pulses intermittently to provide a conductive path between the source of direct-current voltage and the voltage gradient means;

(b) a target of material characterized by low secondary emission of electrons located adjacent the normal path of the cathode ray beam and connected to the voltage gradient means; and

(c) auxiliary beam deflection means connected to the source of higher frequency pulses and responsive to the pulses therefrom to direct the cathode ray beam at said target, whereby the voltage of the voltage gradient means is varied in controlled increments during the interval between pulses from the source of low frequency pulses.

2. In a compact image display system having a cathode ray beam, horizontal beam deflection means, vertical beam deflection means including voltage gradient means arranged to position said beam in dependence upon the voltage of said gradient means, a source of low frequency pulses, a source of higher frequency pulses and a source of direct-current voltage, the improvement comprising:

(a) a switching device having one major electrode connected to the source of direct-current voltage and another electrode connected to the voltage gradient means;

(b) means connecting the source of low frequency pulses to a control electrode of said switching device intermittently to provide a highly conductive path between said major electrodes in response to the pulses from the source of low frequency pulses;

(c) a target of material characterized by low secondary emission of electrons located adjacent the normal path of the cathode ray beam and connected to the voltage gradient means; and

(d) auxiliary beam deflection means connected to the source of higher frequency pulses and responsive to the pulses therefrom to direct the cathode ray beam at said target, whereby the voltage of the voltage gradient means is varied in controlled increments during the interval between pulses from the source of low frequency pulses.

3. An image display system comprising a screen adapted to provide a visible phenomenon in response to excitation by a cathode ray beam; an electron gun arranged to provide a cathode ray beam; magnetic means adapted to provide horizontal scanning of said screen by said beam; electric field beam deflection means including voltage gradient means arranged to position vertically said beam on said screen in dependence upon the voltage of said gradient means; a switching device having an anode and a cathode, said anode being connected to a source of directcurrent voltage and said cathode being connected to said voltage gradient means; a control electrode for said switching device, said control electrode being connected to a source of low frequency narrow pulses and responsive to the pulses therefrom to establish conduction between said anode and said cathode; a target of material characterized by low secondary emission of electrons located adjacent the normal path of said beam and connected to said gradient means; and, auxiliary electric field beam deflection means connected to a source of high frequency pulses and responsive to the pulses therefrom to direct said beam at said target, whereby the voltage of said gradient means and the vertical position of said beam on said screen are varied in controlled increments during the interval between pulses from said source of low frequency narrow pulses.

4. The system of claim 3 wherein said source of low frequency narrow pulses is a source of vertical synchronizing pulses.

5. The system of claim 4 wherein said source of high frequency pulses is a source of horizontal synchronizing pulses and said beam is directed at said target during the interval between horizontal scans of said screen.

6. The system of claim 3 wherein said target and said auxiliary electric field beam deflection means are located between said magnetic means and said electric field beam deflection means.

References Cited by the Examiner UNITED STATES PATENTS 1,976,400 10/34 Ilberg 315-21 DAVID G. REDINBAUGH, Primary Examiner. 

1. IN A COMPACT IMAGE DISPLAY SYSTEM HAVING A CATHODE RAY BEAM, HORIZONTAL BEAM DEFLECTION MEANS, VERTICAL BEAM DEFLECTION MEANS INCLUDING VOLTAGE GRADIENT MEANS ARRANGED TO POSITION SAID BEAM IN DEPNDENCE UPON THE VOLTAGE OF SAID GRADIENT MEANS, A SOURCE OF LOW FREQUENCY PULSES, A SOURCE OF HIGHER FREQUENCY PULSES AND A SOURCE OF DIRECT-CURRENT VOLTAGE, THE IMPROVEMENT COMPRISING: (A) MEANS RESPONSIVE TO THE PULSES FROM THE SOURCE OF LOW FREQUENCY PULSES INTERMITTENTLY TO PROVIDE A CONDUCTIVE PATH BETWEEN THE SOURCE OF DIRECT-CURRENT VOLTAGE AND THE VOLTAGE GRADIENT MEANS; (B) A TARGET OF MATERIAL CHARACTERIZED BY LOW SECONDARY EMISSION OF ELECTRONS LOCATED ADJACENT THE NORMAL PATH OF THE CATHODE RAY BEAM AND CONNECTED TO THE VOLTAGE GRADIENT MEANS; ANS (C) AUXILIARY BEAM DEFLECTION MEANS CONNECTED TO THE SOURCE OF HIGHER FREQUENCY PULSES AND RESPONSIVE TO THE PULSES THEREFROM TO DIRECT THE CATHODE RAY BEAM AT SAID TARGET, WHEREBY THE VOLTAGE OF THE VOLTAGE GRAIDENT MEANS IS VARIED IN CONTROLLED INCREMENTS DURING THE INTERVAL BETWEEN PULSES FROM THE SOURCE OF LOW FREQUENCY PULSES. 